This invention relates to equipment for target ranges and, more specifically, to movable track-mounted target carriers having onboard electrical equipment to which power must be supplied from an external source. The invention also relates to induction-based electrical power transmission systems.
Movable target systems typically employ a target carrier that is movable along a rail or track. There is often a requirement that the target attached to the carrier be movable (e.g., pivotable about its vertical central axis). The provision of linear movement to the carrier and movement to the target with respect to the carrier has resulted in various movable target system designs.
One solution to providing linear movement to a carrier and pivotal movement to a target makes use of a pair of parallel conductor strips mounted on the track which are electrically insulated from one another and between which a voltage potential is applied. Alternatively the track itself may serve as one of the conductors (typically at ground potential) and a single conductor strip or wire insulatedly mounted along the track serves as the other. In either case, the carrier is equipped with brushes or rollers which pick up electrical power from the conductors as the carrier moves along the track, much as a toy electric train derives its power from the rails. Such an arrangement is depicted in U.S. Pat. No. 3,128,096 to C. G. Hammond, et al. Power may be supplied to a first electric motor which drives the carrier along the track, as well as to a second electric motor which is used to pivot the target. Such a design suffers from the drawback that bullet fragments and other debris may alight on the conductor strips and thereby interfere with the electrical connection between the brushes and the conductor strip. Arcing between the brushes and the conductor strips will result in the formation of oxides which will increase the resistance at the connection and result in lower voltages being supplied to the electric motors. In addition, the brushes tend to wear with use, requiring periodic monitoring and replacement to prevent harmful arcing conditions.
Another design employed to provide linear movement to a carrier and pivotal movement to a target is depicted in U.S. Pat. No. 3,614,102 to J. Nikoden, Sr. A first insulated, single-conductor cable has one end spooled clockwise on a rotatable take-up drum which moves laterally about its central axis on a threaded shaft as the drum rotates. The opposite end of the cable is connected to a target carrier, providing motive force in one direction along a track and one conductor for power at the carrier. A second insulated cable has one end spooled counterclockwise on the rotatable take-up drum and the opposite end connected to the target carrier, thus providing motive force in a direction opposite that provided by the first cable and a second conductor for power at the carrier. The pitch of the threads on the shaft is equal to the diameter of the first and second insulated cables. One of the cables wraps around an idler pulley at the end of the track opposite the take-up spool mechanism. Such a design is rather complex and requires constant frequent lubrication of the threaded shaft and brush type contacts to transfer current to each cable at the take-up spool.
Still another design used to provide linear movement to a carrier and pivotal movement to a target utilizes a folded power cable which is dragged behind the carrier. Such a target system design is depicted in U.S. Pat. No. 4,889,346 to Donald M. Destry, et al. Computer printers having a track-mounted, movable print head have a similar cable connection arrangement. As the print head slides on its track, a ribbon cable having conductors encased in a resilient plastic sheath automatically folds upon itself and unfolds as the print head moves. Electricity for both a linear motion motor and a target pivoting motor are provided by the power cable which is attached at one end to the carrier, and at the other end to a power source. Abrasion to the insulated sheath covering the cable caused by frequent movement of the cable, as well as fatigue and eventual breakage of the cable conductors caused by frequent flexing of the cable are significant problems of this design. Another problem relates to the need to provide a mechanism which will maintain the power cable (which is no lightweight ribbon cable) neatly folded as the carrier moves toward the cable power source, regardless of the carrier""s position on the track.
What is needed is a simple and reliable new system for providing linear movement to a track-mounted carrier and pivotal movement to a target attached to the carrier which dispenses with contact brushes, complicated cable spooling/despooling equipment, and folded power cables.
The present invention is embodied in an improved movable target system which meets the need heretofore expressed. Power is inductively transferred to a target carrier movable between first and second locations. The transferred power is used to power electrical equipment on board the target carrier. The electrical equipment may include electric motors, lights, solenoids, and control circuitry for the motors and solenoids. Preferred embodiments of the invention are implemented as track-based systems, as the track provides not only stability to the target carrier, but also protection from stray bullets to the conductive cable.
For a first embodiment of the invention, power is transferred to a target carrier via a stationary inductor and a movable cable, which also provides motive force to the target carrier. An idler pulley is mounted at one end of a track or rail, and a drive motor having a drive pulley is mounted near the opposite end thereof A target carrier, having an onboard power requirements, such as an electric target-pivoting motor, is movably mounted on the track or rail. A first end of an electrically-conductive drive cable is anchored to the carrier, and also connected to a first power-input terminal on the carrier. From the anchoring point on the carrier, the cable extends directly to the drive pulley. The cable wraps around the drive pulley, thus reversing directions. From the drive pulley, the cable extends all the way to the idler pulley, wraps around the idler pulley, and returns to the target carrier to which the second end of the cable is also anchored. However, the second end of the cable is connected to a second power-input terminal on the carrier, which is electrically insulated from the first power-input terminal. The drive cable, at some point along its length, passes near a stationary inductor. For preferred embodiments of the invention, the drive cable passes through the stationary inductor, which is a closed-loop ferromagnetic core, such as a toroid, having at least one turn of wire passing through the core""s aperture. When an alternating current is applied to the stationary inductor, an alternating current of the same frequency is induced in the drive cable. This induced current, received at the first and second power-input terminals, is used to provide the target carrier""s onboard power requirements. Some of the induced current may be rectified, filtered and regulated to provide DC power at the target carrier. The frequency of the applied alternating current may be modulated in order to send control signals to the target carrier. Microprocessor-based circuitry on board the target carrier decodes the modulated AC signals and converts them to binary signals which may be used to directly control functions on board the target carrier. Although not presently considered to be a preferred implementation of the invention, at least this first embodiment of the invention may be implemented as a trackless design by maintaining the cable taut, and suspending the target carrier directly from the cable.
For a second embodiment of the invention, power is transferred to a target carrier via a stationary cable and an inductor movable with the target carrier. One end of a conductive cable is connected to one terminal of a stationary alternating current source that is mounted near one end of an electrically-conductive track or rail having a channel which extends the length of the track, and to which the other terminal of the alternating current source is connected. The cable is routed within the channel to the target carrier, at which point it passes beneath a first in-channel guide pulley that is rotatably mounted on the target carrier. The cable then leaves the channel and passes over at least one out-of-channel guide pulley that is rotatably mounted on the target carrier. While the cable is outside the channel, it passes near or through an inductor affixed to the target carrier. For preferred embodiments of the invention, the drive cable passes through the inductor, which is a closed-loop ferromagnetic core, such as a toroid, having at least one turn of wire passing through the core""s aperture. The cable is then routed beneath a second in-channel guide pulley that is rotatably mounted on the target carrier. From there, the cable is routed to an anchoring device at the opposite end of the track, which may incorporate a cable tensioning device. The cable anchoring device is electrically connected to the track. As the target carrier moves along the track, the guide pulleys mounted on the target carrier lift a short section of the cable from the track. When an alternating current is applied to the cable, an alternating current is induced in the inductor affixed to the carrier. The channel acts much like the outer conductor of a coaxial cable, in that its electromagnetic shielding minimizes power losses caused by energy radiated from the cable. For this second embodiment of the invention, electrical equipment on board the target carrier includes a drive motor for moving the carrier bidirectionally along the track. Thus the current induced in the inductor affixed to the target carrier is used to power not only the drive motor, but any other electrical equipment that may be on board the target carrier, such as motors which move the target with respect to the carrier. Some of the induced current may be rectified, filtered and regulated to provide DC power at the target carrier. Communications with the target carrier may be achieved by modulating the frequency of the applied alternating current. For a preferred embodiment of the invention, modulation involves alternating between two distinct frequencies so that a stream of serial binary data may be sent to the target carrier. Microprocessor-based circuitry on board the target carrier decodes the modulated AC signals and converts them to binary signals which may be used to directly control functions on board the target carrier. For example, the decoded signals may direct the drive motor to move the carrier forward or backward, or direct a target-pivoting motor to rotate the target to a desired position. Return communication for such information as hits on the target or status information can be effected by modulating the load at the coil at a frequency different from that of source alternating current. This modulation will be reflected in measurable current flow fluctuations at the alternating current source. These fluctuations can be decoded in much the same manner that frequency modulation is decoded by the circuitry on board the target carrier.